1. Field of the Invention
This invention relates to a vibration-damping material consisting of two metal plates and a vibration-damping layer of thermoplastic resins interposed between them. More particularly, it relates to a vibration-damping material with extremely high vibration-damping ability and excellent workability in deep drawing, bending, etc.
2. Description of the Prior Art
In recent years, the influence of noise caused by transportation means such as automobiles and railway cars or of noises and vibrations generated at factories and construction sites upon residents in the neighborhoods is becoming more and more serious incurring a big social problem.
As one means for solving the problem, research and development on vibration-absorbing materials having a vibration-absorbing ability by themselves have been made and, as a result, vibration-damping materials having a high vibration-absorbing ability and suitable for various application purposes are already in use as structural members of vehicles, vessels, industrial machines, iron bridges and the like.
As to the noise from automobiles, much noise is generated from parts around the engine, particularly from an oil pan, and its reduction has been strongly required.
As such vibration-damping materials, there have hitherto been known metal/resin/metal multilayer structures using, for their middle layer, a composition such as vinyl acetate-ethyl acrylate copolymer (Japanese patent publication No. 35662/1970), a copolymer obtained by grafting a vinyl acetate-ethylene copolymer with a mixture of styrene and acrylonitrile (Japanese patent publication No. 17064/1971) and a resin composition comprising mainly polyolefin type resin modified with carboxylic acids [Japanese patent application Kokai (laid-open) No. 80454/1984]; or materials composed of a bitumen and a filler such as calcium carbonate.
However, though these vibration-damping materials each show a vibration-absorbing ability in a particular temperature region they have drawbacks in vibration-damping property in that they do not show a sufficiently high vibration-damping ability in temperature regions necessary for various practical applications or they show such high vibration-damping ability only in a narrow temperature region. Moreover, such multi-layer structures have various drawbacks including poor deep drawing or bending characteristic in mechanical pressing (due to insufficient bonding with metal plates, small modulus of elasticity of middle layer composition, etc.), and poor heat resistance. Thus, they are insufficient in secondary workability as vibration-damping metal plates.
The conventional vibration-damping metal plates have various drawbacks in workability in mechanical pressing, etc. In deep drawing, for example, metal plates cause slippage at the ends and, in an extreme case, the two, upper and lower layer, metal plates come off the middle layer vibration-damping resin and cause separation. Further, the low modulus of elasticity in shear of the resin layer causes problems such as surface waviness of shaped articles and wrinkle formation at curved corner surfaces. In severe 180.degree. bending (so-called hemming) which is applied to the ends of vibration-damping metal plates, waviness and wrinkles appearing on the surface of metal plates become more serious making these metal plates unusable in practical applications.